Ok I had another idea about the fusion story
So when Wulan realizes Her season powers represents Her past lives . The way and order each season got released could also mean who they were. Spring is the leader so it could mean that she was the first life and She must have been a queen/empress or a great ancient leader from another planet . Summer being the second season and representing water and sun , She must have been a powerful spirit who controls both water and light and must have been a guardian of a planet . Snow is the third element to be released and She must have been a great and powerful mage whose wisdom was SO POWERFUL that She might have had some connections with the former Ice element master . And for Autumn, She is Re'taka's sister , hence She is the last season .
Hope this gives you some inspo or idea